Behavior of oceanic currents in shelf regions

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The Tsushima Current, the Soya Current and the Tsugaru Current flow in shallow shelf regions. The nature of these current is quite different from currents flowing open ocean, as their current keeps its considerable magnitude down to bottom and they receive significant friction form bottom. Knowledge of the currents in shelf regions is very limited though demands for it has been increased recently. Basic nature of the currents in shelf regions was studied through tank experiment, numerical modelling and data analysis. Dependence of current structure on the relative angle between coast line and inflow are examined. We succeeded to reproduce the current having shape of narrow band along the coast like the Soya Current when the inflow is directed to right and parallel to coast line, and the current with large eddy off the strait mouth like the Tsugaru Current when inflow direction is rectangular to the coast. Most interesting feature is observed when the inflow is directed towards left. The elliptic eddy is produced on front of strait mouth and the eddy rotates clockwise. The eddy is very unstable and breaks down in rather early stage. The detailed nature of the elliptic eddy was examined. The behavior of this complicated eddy motion seems to give some explanations of changeable feature of the Tsugaru Current and the Tsushima Current. We developed numerical two layer model which is applicable for local oceans with bottom topography. Though the application of the model has made only for specified phenomena in the present stage, the model was showed effective for the analysis of currents in shelf region. The data analysis was made for tidal records and temperature records taken on coastal stations and on board of regular liners. Results indicate that these can be used for monitoring oceanic currents in shelf regions.